Life at Low Reynolds Number

A world without coasting

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• At low Reynolds number, there is no coasting: motion stops as soon as the force does.
• Low-Re flows are reversible, so back-and-forth strokes give no net motion.
• Microbes swim with rotating or asymmetric strokes.

Steps

1. No momentum
2. Unmixing
3. The scallop theorem
4. Swimming in honey
5. A sperm cell’s Reynolds number
6. From bacteria to whales
7. A spinning motor